AU2002240916B2 - Marine propulsion system - Google Patents

Abstract

The present invention relates to a vessel propulsion system and, more specifically, to a vessel propulsion system with improved efficiency and which leads to reduced wave formation, which comprises a propulsion device immersed at least partially in water and which rotates about at least one axis of rotation essentially extending perpendicularly to the propulsion device, as well as a cover partially enclosing the propulsion device, whereby the cover and the propulsion device together form a water conveying flow channel when the propulsion device is operated.

Description

-1- Vessel Propulsion System The present invention is in the field of propulsion of watercraft and relates to a vessel propulsion system.

As in all technical fields, also the shipbuilding industry is making an effort to raise the efficiency of a vessel's propulsion system. In addition, especially for inland navigation, there is an increasing need to provide fast vessels that create the smallest possible waves at high speed. It has been demonstrated that waves beating against the shore banks not only impair the reinforcements along them, but also harm the biotopes located at the shore, and in particular disturb the hatching behaviour of birds in habitats nearby.

In addition, especially inland navigation faces the problem of having to avoid pollution caused by lubricants necessarily used for rotating parts of a vessel propulsion system, whereby such lubricants can be released into the water if these parts lie below the water surface during operation of the vessel propulsion system. Almost all known motor or engine driven vessel propulsion systems face this problem.

The object of this invention is to provide an efficient vessel propulsion system that also takes the above problems into account.

This object is solved by a vessel propulsion system according to the invention exhibiting vessel propulsion system with a propulsion device at least partially immersed in water, whereby such propulsion device rotates at least about one axis of rotation essentially extending perpendicularly to the direction of propulsion; and with a covering partially enclosing the propulsion device, characterized in that the covering is arranged relative to the propulsion device such that, during operation of the propulsion device, a gap formed between the covering and the circumferential surface of the propulsion device is completely filled with water and a flow, circulating in the gap in the direction of rotation of the propulsion device, is formed.

The vessel propulsion system according to a preferred embodiment of the invention has a propulsion device, for example a rotatably driven wheel or a driven revolving belt. This rotating or revolving propulsion device is enclosed at its outer circumferential surface by a covering which, however, does not enclose the entire circumference of the propulsion -2 device. On the contrary, the propulsion device comes directly into contact with the surrounding water below the waterline of the vessel to be driven. With the vessel propulsion system according to a preferred embodiment of the invention, the distance between the covering and the propulsion device is chosen such that, when the propulsion device is operated, the water surrounding the vessel is conveyed by the propulsion device into the gap between the front end of the propulsion device and the covering and the air therein is forced out of the gap. This applies at least, as described below in more detail, in the case to be considered as a preferred embodiment, where the covering extends below the waterline independent of the loading condition of the vessel and the upper edge of the covering is arranged above the waterline also independent of the loading condition of the vessel in other words, where also air is at least present between the circumferential surface of the propulsion device and the covering before the propulsion device is operated.

When the propulsion device is operated, the water conveyed by the propulsion device into the gap between the front end of the propulsion device and the covering is conveyed along with the propulsion device in the direction of rotation. Operating the propulsion device thereby results in the formation of a flow channel in the gap, in which the water is being conveyed in the rotating direction of the propulsion device.

The efficiency of the device according to a preferred embodiment of the invention was evaluated in a static pull test by its inventor. For such a test, either the vessel or a model thereof is fixed to a post, with a load cell mounted in-line, to determine the traction force per unit of power. With conventional propellers commonly also referred to as marine screws, a power output of about 0.023 kg/W can be determined in a static pull test of this type. In comparison, the vessel propulsion system according to the invention generated a maximum output of 0.054 kg/W. This maximum output was reached with the vessel propulsion system according to the invention when the flow channel was full of water.

Accordingly, the vessel propulsion system according to the invention offers an essentially higher degree of efficiency compared to the known vessel propulsion systems.

Practical experiments have in addition shown that at the same driving performance, i.e.

the same speed of the vessel model, the vessel propulsion system according to a preferred embodiment of the invention generated a markedly smaller stern wave than that generated by a conventional propeller drive, which specifically takes the requirement for 3 reduced wave formation, particularly for inland navigation, into account. However, the vessel propulsion system according to the invention can be applied effectively not just for vessels for inland navigation.

Although with the vessel propulsion system according to one embodiment of the invention, for example, a propulsion device revolving in a belt-shaped manner may be provided, which may revolve either on a circular track or in the manner of a tank chain with two opposingly situated linear sections and two opposingly situated semicircular sections, whereby such propulsion device is arranged both outside and inside, at a distance to a casing wall, in a water bearing channel, for simplification of the construction of the vessel propulsion system it is proposed to form the propulsion device with a circumferentially closed circumferential surface. In this case, water circulating in the propulsion direction is, in the radial direction of the propulsion device, exclusively present between the outer circumferential surface of the propulsion device and the covering.

The build-up of a flow channel as fast as possible, that conveys water in the direction opposite to that of the direction of propulsion after starting the propulsion device, is achieved in that the flow channel is narrowly limited laterally. The propulsion device may have appropriate contours on its circumferential surface for this purpose. However, according to a preferred further development and to simplify the constructive embodiment of the vessel propulsion system, it is proposed that the circumferential surface of the propulsion device be bordered laterally with bounding elements extending beyond the circumferential surface and almost up to the covering. These bounding elements can be arranged, according to a preferred further development of the invention, either stationarily like the covering, for instance directly on the vessel hull, or at least stationarily relative to the vessel hull. Alternatively it is proposed to connect the bounding elements to the rotating propulsion device.

In order to fill the flow channel on starting up the propulsion device, and also from the viewpoint of efficiency, it has been found advantageous to arrange several teeth one behind the other on the outer circumferential surface of the propulsion device.

These teeth should be formed such that they help to transport the water from the surroundings into the gap between the front end of the propulsion device and the covering. The efficiency of the vessel propulsion system with different directions of rotation can be influenced by the teeth geometry. For example, if the vessel propulsion system according to the invention is used in a vessel as a cross-drive for manoeuvring, and if it is therefore important to achieve the same efficiency in both directions of rotation of the propulsion device, preferably teeth with identically formed leading and trailing edges are arranged on the circumferential surface of the propulsion device.

With a vessel propulsion system with a preferential rotation direction as propulsion direction the teeth formed on the outer circumferential surface of the propulsion device are preferably formed similar to saw teeth, i.e. the leading and trailing edges of the teeth have different inclinations. It has been found advantageous for the leading edge directed radially outwards to the tooth tip to have a smaller inclination than that of the trailing edge adjoining such leading edge on the rear side of the tooth tip and from there directed radially inwards. The trailing edge can even have a sharply radial gradient inwards, i.e. it does not contribute to the circumferential surface. The situation is, however, different for the leading edge. By its ramp-shaped gradient, particularly with a rotating direction of propulsion, the surrounding water is to be pressed into the gap between the covering and the circumferential surface of the propulsion device.

When the propulsion device is started, such a ramp-shaped inclination of the leading edge accordingly results in a relatively rapid formation of the flow in the flow channel.

Practical experiments have further shown that it is advantageous to form the tips of the teeth with an arcuate profile in the axial direction, as proposed in a preferred further development of the invention.

Additionally, it has also been found advantageous to form the leading edge and/or the trailing edge of the teeth with an arcuate profile in the axial direction. Moreover, it is preferred to form the leading and/or trailing edges of the teeth with an arcuate convex profile in the circumferential direction, whereby a combination of the two preferred measures mentioned above, i.e. a spherical embodiment of the leading and/or trailing edges, is viewed as advantageous with respect to the efficiency of the vessel propulsion system and also for the avoidance of waves.

As described above, with regard to the starting behaviour of usual motors for vessel propulsion systems, it is preferable to arrange the upper edge of the covering above the vessel waterline and to allow the front and/or rear ends of the covering to extend below the waterline. With such an embodiment, and if the vessel propulsion system is not in operation, air also exists in the gap between the propulsion device and the covering, which is initially forced out by the ingress of water into the gap when the propulsion device is started. As long as there is air in the flow channel, however, the resistance of the propulsion device to rotation is relatively low. This suits the low starting torque of the usual motors in vessel propulsion systems.

With respect to efficiency, it has been found advantageous for the amount of water drawn into the gap between the propulsion device and the covering to be draw into the gap and removed out of it at a relatively high ratio of horizontal velocity. On the other hand, it should be possible for a specific circumferential section around the propulsion device to freely communicate with the surrounding water. It has been found that the preferred wrapping angle of the covering around the propulsion device is between 2000 and 2700. Additionally, according to a preferred further development of the invention, it is proposed that the end of the covering that forms the inlet for the flow channel be formed with a curvature directed forwards and/or that the end of the covering that forms the flow channel's outlet have a curvature directed rearwards. For attaining good efficiency, it has been further found advantageous to provide a minimum gap between the propulsion device and the covering of a size of 2% to 10%, preferably 3% to of the diameter of the rotating propulsion device. The minimum gap in the previously stated sense, with the preferred embodiment mentioned above with teeth the tips of which have a convex curvature in the axial direction, occurs where the distance between the teeth tips and the covering is at a minimum. It should be noted here that the covering for attaining good efficiency can be formed relatively simple, preferably across from the circumferential surface of the propulsion device, preferably evenly in the axial direction. When a wheel is used as the propulsion device, the covering is thus formed cylindrically but open in one circumferential section.

In view of the best possible effective steering of a vessel provided with the vessel propulsion system, it is further preferred to arrange the propulsion device perpendicular to its axis of rotation and supported rotatably about a steering axis, and to also provide a control device to control the rotation of the propulsion.device about the steering axis.

With such a preferred embodiment, the driving direction can be influenced by rotating the propulsion device about the steering axis without the need for arranging, in addition, a rudder on the vessel. Furthermore, the maximum efficiency of the propulsion device can be utilized in both the reverse and forward driving directions through appropriate rotation of the propulsion device.

To seal the propulsion device appropriately and simply and, if applicable, a driving motor arranged relatively close to the propulsion device, it is preferred to arrange the propulsion device together with the covering on a support plate through which the propulsion device protrudes, which plate in turn is sealed on top with a hood. The hood, accordingly, encloses at least the propulsion device, but not necessarily a possible motor and lubricated bearings or such. When the vessel propulsion system is operated, occasionally there is water within the hood and in the propulsion device area. Here, however, there are no parts lubricated with lubricant so that no lubricant can be released into the surrounding water from within the hood.

In this preferred further development, the support plate is accommodated in a pan that is rotatably supported in the vessel hull and open on the bottom, and the propulsion device protrudes through it, whereby a seal is provided between the support plate and the pan. This seal can, for example, be formed by a bellows. In this embodiment, the surrounding water comes merely to the underside of the pan, the underside of the cover plate and into the area sealed by the hood. Lubricant contamination of the water through contact with lubricated components can thus be avoided, for example, by making all the bearing components of a drive shaft or axis of rotation watertight by the hood.

The aforementioned preferred embodiment is accordingly further developed preferably in that the hood forms the covering. In this case, the section of the hood radially surrounding the propulsion device serves simultaneously as the covering to limit the gap around the circumference of the propulsion device.

To compensate for the gyroscopic forces generated when the propulsion device rotates under full power, it is further preferred to arrange the support plate with a pivoting means on the pan such that at least one inclination attenuator is connected in-line. The gyroscopic forces that develop when the propulsion device is pivoted about the steering axis can thereby be counteracted through certain pivoting of the support plate against the resistance of the inclination attenuator, thereby preventing these forces from being directly transferred on to the vessel hull.

The behaviour of the vessel propulsion system according to the invention can be controlled, according to a preferred further development, in that a gap setting mechanism is provided for adjustment of the distance between the propulsion device and the covering. With this gap setting mechanism, the height of the flow channel can be altered in the vessel propulsion system according to the invention, for example in order to influence the quantity of water flowing around in the flow channel at a constant motor speed (operating point of the driving motor). Therefore, the formation of waves at the vessel stern can be changed without having to change the operating point of the driving motor.

To adapt the vessel propulsion system to different navigation channel depths, especially for inland navigation, according to a preferred further development of the invention it is proposed to include an immersion depth adjustment device for height adjustment of both the propulsion device and covering. By such an adjustment device the depth to which the propulsion device is immersed in the surrounding water can be influenced without simultaneously altering the gap that forms the flow channel. An immersion depth adjustment device of this type is especially preferred if the propulsion device protrudes beyond the bottom of the vessel hull. In particular, with propulsion devices for vessels navigating in very shallow waters or vessels that run aground with the tides, whose propulsion means, due to this, should nevertheless not be damaged, it is quite conceivable to form the propulsion device such that the axis of rotation extends in the vertical direction, i.e. the propulsion device protrudes through the side of the vessel.

With the usual arrangement of the propulsion device on the underside of the vessel hull, in view of the best possible buoyancy of the vessel, especially for fast driving full glider boats, it is preferable to provide on the front ends of the propulsion device in each case at least one float tapering down from the propulsion device preferably in the axial direction of the axis of rotation. A float tapered in such a way is preferably attached directly to the front end of the propulsion device and has a diameter in this area equal approximately to that of the propulsion device. For reasons of flow dynamics, the diameter tapers in the axial direction of the axis of rotation, whereby the float is formed preferably conical in shape, with an outer surface initially convex in curvature adjoining the propulsion device and followed by a straight outer surface or by one which is concave in curvature. A float formed in this way, preferably formed as an enclosed hollow body, results, however, not only in better buoyancy of the vessel, but also, in addition, raises the vessel during its motion and due to the forces counteracting the float. In order to avoid frictional losses between the oncoming water stream and the float, and thus raise efficiency, it is furthermore preferred to arrange the float such that it is freely rotatable on the axis of rotation or on the drive shaft of the propulsion device.

It has been found advantageous particularly with fast driving full glider boats to provide a thickening on the radial outer end of the propulsion device. This thickening, which is connected to the propulsion device and covers the propulsion device in a mushroomhead-like manner, protrudes beyond the circumference of the float at least partially. It has been found that, due to the high efficiency of the vessel propulsion system according to the invention, vessels formed as glider boats and supported by the buoyancy effect of the floats can rise far enough out of the water at full power that they essentially stay in contact with the water merely through the mushroom-head shaped thickenings. Preferably, the vessel propulsion systems according to the invention are for this purpose provided such that two propulsion systems in each case are arranged at the vessel's front end and two at its rear. In this case, the in total four propulsion devices simultaneously form the propulsive parts at full power as well as those parts which, for example, with a hydroplane, carry the vessel's load on the water. In this regard it is preferred to form the mushroom-head shaped thickening as hydrodynamic as possible such that its outer circumferential surface preferably forms the continuous continuation of the outer circumferential surface of the float.

Further details, advantages and characteristics of this invention become apparent from the following description of embodiments in conjunction with the drawing, the figures of which show the following: Figure 1 shows a side view of a vessel with a first embodiment of a vessel propulsion system according to the invention; Figure 2 shows a bottom view of the vessel depicted in Figure 1; Figure 3 shows a front view of the embodiment depicted in Figure 1 with the covering partially cut away; Figure 4 shows the sectional view IV-IV according to the illustration in Figure 3; Figure 5 shows a side view of a vessel with a further embodiment of the vessel propulsion system according to the invention; Figure 6 shows a bottom view of the vessel depicted in Figure 5; and Figure 7 shows a partial front view of the embodiment of a vessel propulsion system depicted in Figure 6.

Figure 1 depicts a side view of a vessel 2 formed as displacement vessel for different immersion depths. The different immersion depths are recognizable from the different waterlines W for different loading conditions. At the stern of vessel 2 there is a vessel propulsion system 4 according to the first embodiment of the present invention. As essential components of this vessel propulsion system 4 a propulsion device formed as a toothed wheel 6 as well as a covering 8 circumferentially enclosing the toothed wheel 6 at least partially are provided. The axis of rotation 10 of the toothed wheel 6 extends, in the embodiment shown, in the horizontal direction and otherwise perpendicularly to the direction of propulsion V, i.e. at right angles to the longitudinal axis of the vessel 2.

The covering 8 is formed cylindrically, i.e. with surfaces extending sideways parallel to the axis of rotation 10. The covering 8 encloses the toothed wheel 6 with a wrapping angle of about 2400. The covering 8 has a front end, i.e. bow end, 12, and a rear end, i.e. stern end, 14. Both ends 12, 14 terminate at about the same height and are flush with the underside of the vessel hull 16. Between the two ends 12, 14, the toothed wheel 6 protrudes beyond the underside of the vessel hull 16.

In the bottom view of the vessel hull 16 according to Figure 2, the accommodation space for the toothed wheel can be recognized clearly. This accommodation space is circumferentially limited by the covering 8 and laterally formed by stationary sidewalls 18, 20. The sidewalls 18, 20 are connected to the vessel hull 16 and are protruded through by the drive shaft 22 located in the axis of rotation of the toothed wheel, as described in the following in more detail and making reference to Figure 3.

Figure 3 shows a front'view of the vessel propulsion system as illustrated in Figures 1 and 2. The drive shaft 22 is supported on both sides by bearings 24, 26, respectively.

At one end of the drive shaft 22, behind the bearing 26, there is an angular gear 28 whose end on the side of the force is connected to any desired type of motor 30, such as an electric motor.

The sidewalls 18, 20 form a U-shaped enclosure around the toothed wheel 6, and their undersides are welded to the vessel hull 16. The drive shaft 22 goes through the sidewalls 18, 20 and is sealed against them with appropriate seals. A horizontally extending cross brace 32, running parallel to the axis of rotation 10 of the drive shaft 22, of the hood 34 formed in this way forms the covering 8 partially enclosing the toothed wheel 6 circumferentially. The hood 34 is formed in two parts, whereby the lower part 36 comprises the seal and the duct for the drive shaft 22 and is firmly connected to the vessel hull, whereas the upper part 38, which is connected to and sealed against the lower part 36 with a flange 40, can be removed for maintenance purposes. The' location of the joint between the upper part 38 and the lower part 36 is preferably chosen such as to allow the upper part to be removed under any loading condition without water flowing into the vessel hull 16.

In Figure 3 it can be recognized that the toothed wheel 6 is laterally bordered by bounding elements 42, 44. These bounding elements 42, 44 are ring-shaped and are firmly connected to the rotating toothed wheel 6. With their radial outer ends the bounding elements 42, 44 extend beyond the circumferential surface of the toothed wheel 6 and almost up to covering 8.

The toothed wheel 6 exhibits several teeth 46 on its circumferential surface that have a convex gradient in the axial direction relative to the axis of rotation 10. In Figure 3, the tooth tip 48 of the uppermost tooth 46 is clearly recognizable.

Details of the circumferential design of the toothed wheel are recognizable from Figure 4. This shows a sectional view along the line IV-IV according to the illustration in Figure 3 and particularly serves to highlight the embodiment of the teeth 46. The direction of rotation D in the main direction of propulsion of the vessel, i.e. that particular direction of rotation of the toothed wheel 6 when the vessel moves forward, is marked by a curved arrow D. Each tooth 46 has a leading edge 50 and a trailing edge 52. Relative to the circumference of the toothed wheel 6, the leading edge 50 has a lower pitch than the trailing edge 52. Each tooth 46 of the toothed wheel 6 is identically formed. The leading edges 50 and the trailing edges 52 are convex-shaped relative to the axial extension of the axis of rotation 10. Accordingly, the inner serrated contour in Figure 4 depicts the outer axial outline of the toothed wheel 6, whereas the outer serrated contour in Figure 4 reflects the circumferential contour in the middle (relative to the direction of width of the tooth).

Besides the aforementioned convex embodiments in the axial direction, the leading and trailing edges 50, 52, respectively, are also convex-shaped in the circumferential direction. The outcome is that the edges 50, 52 of the respective teeth 46 are formed spherically. The curvature in the axial direction is shown schematically in Figure 2.

The embodiment shown in Figure 4 has disc-shaped bounding elements 42, 44 between which sheet metal is welded which forms the leading and trailing edges 52. The leading and trailing edges 50, 52 of the teeth 46 form a circumferentially closed circumferential surface on the toothed wheel 6.

The embodiment shown in Figures 1 to 4 is operated as follows: In a non-operative state, i.e. when the toothed wheel 6 is not turning, there is air in the gap 54 above the waterline between the covering 8 and the toothed wheel 6, whereby the shape of the cross-section of this gap changes in the circumferential direction with the pitch of the leading and trailing edges 50, 52. When starting for moving forward (propulsion direction the toothed wheel 6 is rotated in the direction of rotation according to arrow D. Initially the toothed wheel 6 tumrns slowly due to its inertia and carries the surrounding water into the gap 54 by means of the forward leading edge 50 of the respective tooth 46. With an increasing rotation speed of the toothed wheel 6, the air in the gap 54 is fully removed in the rotation direction of the toothed wheel 6. The water flows continuously around in the gap 54 in the rotation direction D. In other words, operation of the toothed wheel 6 results in a water conveying flow channel being formed between the toothed wheel and the covering 8. The current in the flow channel extends from the rear end 14 up to the front end 12 of the channel, i.e. in the direction of propulsion V. The water is conveyed into the gap 54 by the leading edge 50 at a horizontal velocity component which is assumed to be appropriate for moving the vessel forward, and it likewise exits the gap 54 at a horizontal velocity component which is assumed to be appropriate for likewise moving the vessel 2 in the propulsion direction V, i.e. forward.

Figures 5 to 7 show a second embodiment of a vessel propulsion system according to the invention. As shown in Figures 5 and 6, this embodiment is built into a vessel 2 formed as a full glider boat. More precisely. stated, four identical embodiments of the vessel propulsion system according to the invention are built into vessel 2. There are in each case two of the vessel propulsion systems 4a situated in the transverse direction adjacent to each other in the bow of the vessel 2, and two vessel propulsion systems 4b are situated in the transverse direction adjacent to each other in the stem of the vessel 2. With the vessel illustrated in Figures 5 and 6 a separate rudder can be dispensed with, since the vessel propulsion systems are in each case steerable.

Details of this steering arrangement can be seen in Figure 7. For each vessel propulsion system 4 a circular recess 60 is provided on the underside of the vessel hull 16, each bounded by sidewalls 56 extending above the waterline W. In the cylindrical inner space thus formed there is a pan 58 with its sidewall 60 extending parallel to the sidewall 56 of the hull 16. The underside of the pan 58 has a circular recess 62 through which the toothed wheel 6 and the floats 46 protrude, as described in greater detail below. Through the bearings 66, the pan 58 is, relative to the vessel hull, rotatably supported about an axis of rotation S. This rotation of the pan 58 within the vessel hull 16 is controlled by a control device not shown in detail for steering the respective direction of rotation. Each of the propulsion devices 4a, b can be rotated independently of each other about the steering axis S.

The pan 58 accommodates a support plate 68 which also has a circular recess through which the toothed wheel 6 and the floats 64 protrude. The support plate 68 carries the bearings 24, 26 and also the motor 30. Between the base plate of the pan 58 and immediately adjacent to the recess 62 and the support plate 68 a seal formed as a bellows 72 is provided which surrounds the recesses 62, 70, thereby hindering the ingress of water between the base plate 68 and the underside of the pan 58 into the latter.

The hood 34 rises from the side of the support plate 68 pointing away from the water.

Also in this embodiment, the drive shaft 22 protrudes through the hood 34. The bearings 24, 26 are located outside of hood 34.

Also in this embodiment, the toothed wheel 6 is connected to the drive shaft 22 in a torsionally rigid manner, and the bounding elements 42, 44 are likewise provided torsionally rigid to the toothed wheel 6. Located adjacent to the sides of the bounding elements 42, 44 are the respective floats 64 which, through the bearings 74, are supported on the drive shaft 22 in a freely rotatable manner.

The floats 64 are essentially formed identically and have, adjacent to the toothed wheel 6, a diameter which approximately corresponds to that of the latter. The outer contour of the floats 64 is formed as follows in the embodiment shown: A first circumferential section 76 extends parallel to the axis of rotation 10, followed by a second circumferential section 78 which essentially has a plane contour running towards the axis of rotation 10. This second circumferential section 78 can, in view of a buoyancy as great as possible of the floats 64 immersed in water, also be formed in an outwardly convex-shaped manner. The first circumferential section 76 is, on its circumference, surrounded by a thickening 80 firmly connected to the toothed wheel 6. The inside of this thickening 80 is cylindrically formed. The thickening 80 extends on both sides of the toothed wheel 6 and the allocated bounding elements 42, 44 and appears in mushroom-head shape in the sectional view shown in Figure 7. The thickening 80 is continued centrally in the area of the toothed wheel 6 by the surface contour of the teeth 46. The outer contour of the thickening 80 is continuously and without any steps continued by the tooth tip 48 of the teeth.

The support plate 68 is held in the pan 58 and is supported in a pivoted manner relative to the latter, and more specifically by the in-line arrangement of at least one inclination attenuator 82 formed as a conventional telescopic damper. One end of the attenuator 82 is connected to the upper end of the sidewall 60, whereas its other end is linked close to the support plate 68.

The inclination attenuator 82 serves to dampen pivoting movements about a pivot axis extending, in the embodiment shown, in the longitudinal direction of the vessel. The support plate 68 is supported by bearings at its front and rear ends, seen in the propulsion direction, such that it can be pivoted for these pivoting movements. The pivot axis formed in this way runs, in each case, rectangularly to the axis of rotation of the motor 30 and the steering axis S and intersects the two axes at their common point of intersection. With the embodiment shown, this point of intersection is the centre of the toothed wheel 6.

With respect to the embodiment of the gap 54 between the bounding elements 42, 44, the embodiment shown in Figures 5 to 7 corresponds to the previously discussed embodiment of Figures 1 to 4. As such, the prior statements on the operation apply accordingly, but it should be noted here that hood 34 covers a larger area including the floats 64.

When the vessel propulsion system shown in Figure 7 is twisted about the steering axis S, this results, with operation of the vessel propulsion system, in a gyroscopic force due to which the support plate 68 pivots relative to the pan 58. This pivoting motion is dampened by the inclination attenuator 82. Due to this, the support plate 68 is returned to its initial position shown in Figure 2. The inclination attenuator 82 thereby prevents the gyroscopic force from being transferred directly on to the vessel hull.

List of Numbers and Letters Referenced 2 Vessel 4 Vessel propulsion system 6 Toothed wheel 8 Covering Axis of rotation 12 Front end 14 Rear end 16 Hull 18 Sidewall Sidewall 22 Drive shaft 24 Bearing.

26 Bearing 28 Angular gear Motor 32 Cross brace 34 Hood 36 Lower part 38 Upper part Flange 42 Bounding element 44 Bounding element 46 Tooth 48 Tooth tip Leading edge 52 Trailing edge 54 Gap 56 Sidewall 58 Pan Sidewall 62 Recess 64 Float 66 Bearing 68 Support plate Recess 72. Bellows 74 Bearings for the floats 76 First circumferential section 78 Second circumferential section Thickening 82 Inclination attenuator D Direction of rotation S Steering axis V Direction of propulsion W Waterline

Claims (23)

1. Vessel propulsion system with a propulsion device at least partially immersed in water, whereby such propulsion device rotates at least about one axis of rotation essentially extending perpendicularly to the direction of propulsion; and with a covering partially enclosing the propulsion device, characterized in that the covering is arranged relative to the propulsion device such that, during operation of the propulsion device, a gap formed between the covering and the circumferential surface of the propulsion device is completely filled with water and a flow, circulating in the gap in the direction of rotation of the propulsion device, is formed.

2. Vessel propulsion system according to Claim 1, characterised in that the propulsion device comprises a rotatably driven wheel.

3. Vessel propulsion system according to Claim 1, characterised in that the propulsion device comprises a rotatably driven revolving belt.

4. Vessel propulsion system according to one of the previous claims, characterised in that the propulsion device exhibits a circumferentially closed circumferential surface. Vessel propulsion system according to one of the previous claims, characterised in that the circumferential surface of the propulsion device is bordered on its sides by bounding elements protruding beyond such circumferential surface and extending almost up to the covering.

6. Vessel propulsion system according to Claim 5, characterised in that the bounding elements and the covering are arranged stationarily.

7. Vessel propulsion system according to Claim 5, characterised in that the bounding elements are connected to the rotating propulsion device.

8. Vessel propulsion system according to one of the previous claims, characterised in that the outer circumferential surface of the propulsion device has several teeth arranged one behind the other.

9. Vessel propulsion system according to Claim 8, characterised in that each tooth has a leading edge directed radially outwards and a trailing edge extending therefrom, directed radially inwards, and the leading edge has a gradient lower than that of the trailing edge. 19 Vessel propulsion system according to Claim 8 or 9, characterised in that the tooth tip of the teeth is formed as a convex curvature in the axial direction.

11. Vessel propulsion system according to one of the Claims 8 to 10, characterised in that the leading edge and/or the trailing edge of the teeth are formed as a convex curvature in the axial direction.

12. Vessel propulsion system according to one of the Claims 8 to 11, characterised in that the leading edge and/or the trailing edge of the teeth are formed as a convex curvature in the circumferential direction.

13. Vessel propulsion system according to one of the previous claims, characterised in that a rear end of the covering forming the inlet for the flow channel has a curvature directed forwards.

14. Vessel propulsion system according to one of the previous claims, characterised in that the front end of the covering forming the outlet for the flow channel has a curvature directed backwards.

15. Vessel propulsion system according to one of the previous claims, characterised in that the upper edge of the covering is arranged above the waterline of the vessel and the front and/or rear ends of the covering extend below the waterline

16. Vessel propulsion system according to one of the previous claims, characterised in that the covering extends with a wrap angle of between 2000 and 2700 about the propulsion device.

17. Vessel propulsion system according to one of the previous claims, characterised in that between the propulsion device and the covering a minimal gap is formed of 2% to 10%, preferably 3% to of the diameter of the surrounding propulsion device.

18. Vessel propulsion system according to one of the previous claims, characterised in that the propulsion device is, perpendicular to its axis of rotation rotatable about a steering axis and a control device is provided to control the rotation of the propulsion device about the steering axis.

19. Vessel propulsion system according to Claim 18, characterised in that the propulsion device together with the covering are arranged on a support plate through which the propulsion device protrudes, whereby the upper surface of the support plate is sealed by a hood and the support plate is accommodated in a pan 20 O with an open bottom and such pan is rotatably supported in the vessel hull and the rpropulsion device protrudes through the pan and a seal is provided between the support plate and the pan. Vessel propulsion system according to Claim 19, characterised in that the hood forms the covering.

21. Vessel propulsion system according to Claim 19 or 20, characterised in that the O support plate is, using at least one in-line inclination attenuator, supported on the pan such that it can be pivoted.

22. Vessel propulsion system according to one of the previous claims, characterised in that a gap adjusting device is provided for adjusting the propulsion device relative to the covering.

23. Vessel propulsion system according to one of the previous claims, characterised in that it exhibits an immersion depth adjustment device for adjusting the height of the propulsion device and the covering.

24. Vessel propulsion system according to one of the previous claims, characterised in that a float is provided on the front ends of the propulsion device in each case and such float tapers down preferably in the axial direction of the axis of rotation, away from the propulsion device. Vessel propulsion system according to Claim 24, characterised in that the floats are supported in a freely rotatable manner on the axis of rotation or on the drive shaft of the propulsion device.

26. Vessel propulsion system Vessel propulsion system according to Claim 24 or characterised in that on the radial outer end of the propulsion device a thickening is provided which is connected to the propulsion device and which covers the propulsion device in a mushroom-head shaped manner and which, at least partially, circumferentially protrudes beyond the float. 21

27. Vessel propulsion system substantially as herein described with reference to the accompanying drawings. Dated this 19 th day of May 2005 SCHMITT KUGELANTRIEBE GMBH By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia